Process for producing triptane by contacting methanol or dimethyl ether with zinc bromide

ABSTRACT

Method for the production of triptane comprising contacting a reactant selected from methanol, dimethyl ether, or mixtures thereof, with zinc bromide at a temperature of from about 210° to about 245° C.

BACKGROUND OF THE INVENTION

This invention relates to the production of organic compounds,especially hydrocarbons, from starting materials such as methanol,dimethyl ether, and mixtures thereof. More particularly, the inventionprovides a novel process for the production of branched chainhydrocarbons, particularly triptane, from methanol, dimethyl ether, ormixtures thereof.

Prior experimental work with methanol conversion to hydrocarbons may becharacterized as largely academic or substantially un-economic inpresent terms. For example, as early as 1878, LeBel and Greene (Compt.rend., vol. 87, p. 260) produced alkyl hydrocarbons by contactingmethanol with zinc chloride at elevated temperatures. More recently,Grosse and Snyder describe and claim a process in U.S. Pat. No.2,492,984 wherein a mixture consisting essentially of a specified metalhalide and at least one compound selected from the group consisting ofmethanol and dimethyl ether is subjected to conversion conditions,including a temperature of 250° to 650° C, to form substantial amountsof recoverable hydrocarbons having at least four hydrocarbons. Theexamples of the patent employ a zinc chloride catalyst, and thespecification mentions that higher atomic weight halides of metals suchas zinc, cadmium, thorium, and the like, may be used.

However, results reported in the patent are far from satisfactory,insofar as disclosure of suitable yields of high grade gasolinecomponents is concerned. Conversions of up to 50 percent of recoverablehydrocarbons of four carbon atoms, based on the mols of methanol ordimethyl ether converted, are claimed. However, the experimentsdisclosed report, at best, a fraction containing about 20 percent (onthe same basis) of recoverable hydrocarbon material boiling between 25°C at atmospheric pressure and 85° C at 1.5 mm. of Hg pressure (about246° C at atmospheric pressure). No mention is made of the production oftriptane (2, 2, 3-trimethyl butane), a heptane and a valuable fuelcomponent.

The high cost of petroleum-based fuels and the potential availability oflarge quantities of methanol, e.g., methanol derived from synthesis gasor methane, have given rise to efforts to convert this methanol intohigher grade fuels. Because of the superiority of triptane as a blendingagent for high-grade gasoline, a process for producing triptane, as wellas other hydrocarbons, from methanol or dimethyl ether could have greateconomic importance.

SUMMARY OF THE INVENTION

Accordingly, the invention provides a process for the production oftriptane, comprising, contacting a material such as methanol, dimethylether, or mixtures thereof, with an effective amount of zinc bromide ata temperature of from about 210° to about 245° C. In its preferred form,the invention comprises a process for the production of triptane whereinmethanol is contacted with an effective amount of zinc bromide at atemperature of from about 215° to about 240° C.

The source of the methanol employed is a matter of choice. For example,methanol derived from snythesis gas produced from coal, and methanolproduced from natural gas are eminently suited to the practice of theinvention. The purity of the methanol is not critical, provided theimpurities do not interfere with the reaction. Thus, small amounts ofwater and ethanol, common impurities in methanol, do not interfere.Similarly, the presence of small amounts of synthesis gas from asynthesis gas conversion system does not interfere substantially withthe methanol conversion reaction. The degree of purity of the methanolemployed will, of course, affect the quantity of triptane produced, whenconsidered with respect to total volume of feed material to the reactor,but the decision to use greater purity methanol must be viewed in thelight of the increased cost of purification of the methanol prior touse. In general, dilute streams of methanol may be used, provided, asnoted, the diluents do not interfere with the activity of the zincbromide. The term "methanol" as used in the specification and claims, isintended to include the use of such dilute streams containing methylalcohol. Moreover, any material which will react to provide methanol insitu under the reaction conditions specified herein, and which does notinterfere with the reaction, and whose other reaction product orproducts, if any, do not interfere with the conversion reaction, iswithin the scope of the invention. For example, since dimethyl etherdecomposes under the reaction conditions employed to form methanol,dimethyl ether may be used as a source of methanol, either as the totalfeed, or a portion thereof. Under some conditions, disclosed herein,significant quantities of dimethyl ether may be formed. This dimethylether may be separated and recycled, thereby providing a highlyefficient use of source materials.

In the same manner, the zinc bromide employed need not be pure, but maycontain impurities which do not interfere with the reaction. Commercialgrade zinc bromide is acceptable in the process of the invention, andthe low cost of zinc bromide and its ease of recovery are advantages ofthe invention.

The temperatures employed in the reaction are significant. Althoughtriptane is produced in the presence of zinc bromide at temperaturesabove 250° C, greater selectivity of the reaction to triptane isobtained at temperatures of from about 210° to 245° C. As indicated, thepreferred temperature range is from about 215° to about 240° C, withtemperatures of from about 220° to about 235° C being most preferred.Selectivities to triptane are superior, at the general temperaturesindicated, and much superior at the preferred temperatures, to thoseobtained at 250° C or above, even though total quantities of reactionproduct may be roughly the same or even less.

Pressures employed in the reaction zone are not critical, and may varywidely. Thus, pressures may be atmospheric, below atmospheric, orgreater than atmospheric. As a practical matter, pressure in abatch-type system may be atmospheric initially, but will rise astemperatures are raised. Pressures on the order of 2000 p.s.i.g. or evenhigher may be used, and the selection of the appropriate pressure to beemployed is well within the skill of the art.

The ratio of methanol to ZnBr₂ is significant, and an effective amount,i.e., an amount sufficient to initiate and sustain the reaction must beemployed. Those skilled in the art may readily determine appropriateamounts, keeping in mind that excessively high ratios of methanol toZnBr₂ may not be used. For example, ratios of from about 0.01 mol ofmethanol per mol of ZnBr₂ to about 24 mols of methanol per mol of ZnBr₂may be used, while ratios of from about 0.1 mol of methanol per mol ofZnBr₂ to about 10 mols of methanol per mol of ZnBr₂ are preferred. Inthe case of dimethyl ether as a feed, the ratio of feed to ZnBr₂ wouldbe similar, and where dimethyl ether is used as a portion of the feed,adjustment of the ratios may be made accordingly.

The process may be conducted batch-wise or in a continuous fashion.Whichever procedure is employed, good mixing or contact of the ZnBr₂ andmethanol is important for good results. Any reaction system whichprovides a high degree of mixing or contact of the methanol and ZnBr₂may be employed. For example, fixed bed systems, slurry reactors, andtrickle bed reactors may be used. Contact times are not critical, andthose skilled in the art may vary the contact times to providesufficient contact time to produce optimum results, depending on, e.g.,volume of reactants, reactor design, temperature, etc. For example,utilizing a fixed bed reactor design, and continuous flow of reactants,contact times on the order of from about 0.5 minute (245° C) to about120 minutes, or 180 minutes, (225° C), or even longer may be used. Wherebatch procedures are employed, contact times may be considerably longer.In both batch and continuous procedures, it is not necessary that 100percent conversion of the methanol be obtained before recovering theproduct, the methanol being easily separable and recyclable. Thetriptane may be separated from the other reaction products before use,or the reaction products mixture may be used directly as a fuel orblending agent.

DETAILED DESCRIPTION OF THE INVENTION

In order to describe the invention with greater particularity, referenceis made to the following example:

About 200 grams of ZnBr₂ and 40.0 grams (50 ml.) of methanol werecombined under nitrogen in an autoclave and the autoclave was thensealed. The pressure was raised to 200 p.s.i.g. with nitrogen, and themixture was stirred and heated to about 225° C for 1 hour. The reactorwas then cooled to room temperature and the pressure reduced to about210 p.s.i.g. Gaseous product and nitrogen were vented into a waterdisplacement gas holder. Liquid product was distilled from the reactorat about 100° C to a cold trap, first at atmospheric pressure with slownitrogen flow (30 min.), and then at reduced pressure (30 min. at 20mmHg, then 15 min. at 2 mmHg). The material remaining in the autoclave(mainly ZnBr₂) was washed out with water.

Gaseous product was small in amount, and consisted mainly of isobutanewith some higher isoparaffins. Very little methane, ethane, or propanewere found. The liquid product in the cold trap comprised two layers, alower aqueous layer and an upper hydrocarbon phase. The lower layer wasessentially water, very little methanol being present. The hydrocarbonlayer (5.04 grams) gave the following analysis:

    ______________________________________                                        Compounds              Percent by weight                                      ______________________________________                                        isopentane             11.2                                                   isohexanes             13.5                                                   triptane               47.4                                                   other heptanes and                                                            isooctanes             10.8                                                   C.sub.9 to C.sub.13 hydro-                                                    carbons                15.3                                                   CH.sub.3 Br            Trace                                                  CH.sub.3 O CH.sub.3    Trace                                                  ______________________________________                                    

What we claim is:
 1. A method for the production of triptane comprisingcontacting a material selected from the group consisting of methanol;dimethyl ether; other materials which react to provide methanol in situ,other reaction products, if any, being non-interfering; and mixturesthereof, with an effective amount of ZnBr₂ at a temperature of from 210°to 245° C.
 2. The method of claim 1 wherein the temperature is from 215°to 240° C.
 3. The method of claim 1 wherein the temperature is from 220°to 235° C.
 4. A method for the production of triptane comprisingcontacting methanol with an effective amount of ZnBr₂ at a temperatureof from 210° to 245° C.
 5. The method of claim 4 wherein the temperatureis from 215° to 240° C.
 6. The method of claim 4 wherein the temperatureis from 220° to 235° C.
 7. A method for the production of triptanecomprising contacting dimethyl ether with an effective amount of ZnBr₂at a temperature of from 210° to 245° C.